Problem 42316. Fraction of a fraction of a ...

One sort of brainteaser problem is a math problem wherein you are asked what the given fraction of a fraction of a ... number is. For example,

What is one-seventh of two-ninths of 630?

You will be supplied with various strings of this format (minus the "What is" at the beginning and the question mark at the end. Write a function to translate the string and calculate the value. Hyphens will always be present between top and bottom values of fractions while "of" can be replaced by a multiplication symbol. Also, make sure you capture singular and plural fractions. In this case, the translated string might look something like this:

1/7 * 2/9 * 630

which, when evaluated, will yield 20. See the test suite for more examples.